Green technologies and sustainability efforts are important, but scientists say the only way to truly rein in global warming is to attack the issue at its source by reducing carbon emissions, according to a comprehensive new study that coincides with the Obama administration's new proposal to reduce such emissions.

"We found that climate engineering doesn't offer a perfect option," Daniela Cusack, an assistant professor of geography in the University of California, Los Angeles’ College of Letters and Science and the study's lead author, said in a statement. "The perfect option is reducing emissions. We have to...